Resizing UU-2 main jets

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    Ok, one issue with my car is that the UU-2 carburetor seems to have come off a Studebaker and has undersized main jets. I saw a discussion about vapor lock with ethanol gasoline and that upsized jets helps with that issue.

    My question is what diameter is recommended and is it okay to re-drill the cross holes in the jets?


    You need to change the small and large (2) venturies, the idle tubes, main jets, idle air bleeds, and be sure you have the correct lower, air horn, and choke butterflies………….the UUR2 was made for almost 200 applications, yes……200. There are an endless number of different throttle and choke shafts, as well as hardware. Do NOT bolt that thing on and run the car, you will end up melting the valves or burning a hole in a piston.


    Increasing the jet size will NOT help with vapor lock. Your car is 366 CID, the stude carb could fit a engine as small as 198 CID……..don’t take the chance. A few years ago a car at the PAS meet swapped out a carb for someone’s spare when they had a problem, and the piston melted.


    I have to hope your doom & gloom prediction is a bit off… this is the carb from the car that had attended a few PAS meets and tours with the last owner and raced at Watkins Glen with you from other posts here… it hasn’t melted yet.

    Once I get it back out of the cleaner I’ll measure the venturi and compare it to what was listed as the specs in a previous PAS Service Bulletin and see what else is there.


    E10 is already seven percent leaner than regular gas, and the lean condition can also cause the head to crack and the exhaust manifold to split. Doom and gloom, no, but I don’t want to see a car or an owner suffer unnecessarily for a relatively simple repair with parts available very easily. I have been doing this forty years, and my cars all run they way they should. Ask David Coco or Dave Stephens if setting up a carb is important, not only to prevent damage, but have the correct power, idle, and hot start soaking. The car was at the track with me……..yes, I remember it on the tour. I did three Strombergs this week two for Model J”s and one for a DV-32. I have probably done fifty of them, Cislak has done hundreds……… the meet this summer I invite you to drive the car we bring, and see if the throttle response is different from what you are use to. Idle tubes, power valve, idle air bleeds, and several of the springs can all be changed to make the car start and idle much better today with modern fuel. And the car will run cooler. As they say….it’s better to be safe than sorry. Ed


    I didn’t think you would get offended, my apologies…

    My plan is to make it right, and be able to close the choke all the way without it getting too lean. I asked what Cislak got for a rebuild and it’s 1/4+ of what I have in the car and he doesn’t do just a rebuild it has to be done to show quality… which would not look right on an original car IMHO.

    My carb has 046 jets, the PAS service bulletin lists 050 jets. Has anyone else reconfigured a carb to run on a Pierce who will answer this without telling me I’m an idiot that should throw my money at it?

    Thank you.


    Mark, contact Arnold Romberg, he has the specs you are looking for to check your jet and metering valves. He may not be back from the winter board meeting in Branson, but send him an e-mail. His e-mail can be found in the online roster. Karl


    Thank you for the useful information Karl, I appreciate it.

    I spent a half hour on the phone with John at The Carburetor Shop and he went through the books with me to verify that my carburetor was right internally, he also sold me some literature I probably didn’t need but after being that helpful I didn’t mind.

    The carburetor that was on my car is basically a factory setup for the 30 model which is a very similar engine and it seems that drilling the jets up should yield better results. Don’t know if 30 had the large air horn but this one does and lined up perfectly with the air cleaner and inlet tube connected to the engine pan.

    I’ll still contact Arnold as it will be a while before I need it complete again, I plan on looking at the valves and cooling system plus anything else that jumps out while I have the head & oil pan off.


    Mark……not offended. Just want to see your car going down the road in the best possible condition.


    Mark, I’m not sure off the top of my head which size jets and venturies are correct. You definitely want to be in the rich side. I use a five gas analyzer to tune the carb after setting it up. With E10 pump gas you definitely need to add more fuel than stock. Since Pierce was one of the largest CID motors to use the UUR2 most swapped out carbs are undersized as far as the internal components go. I loaned out my Stromberg catalog with all the part numbers and specifications and it didn’t get returned so I can’t look up the numbers for you. You can use the old fashion method of reading spark plugs, but fuel today doesn’t tend to leave much sign of the burn on the electrodes. If your running an electric fuel pump, be sure to keep the pressure on the low side to prevent fires from over pumping, also, too much fuel pressure will cause the car to run too rich.Without starting from a factory stock carb, getting everything right can be very challenging. If the large and small venturies are correct, jetting it is fairly straight forward. If thr carb is way undersized then getting it to perform correctly overall is very difficult. Your best bet would to contact someone with another model 43 and see what they have in their carb. Ed


    Thank you Ed, as I mentioned I spent a good amount of time with John and he went through the UU-2 specs with the book in front of him. The UUR is the correct one and was most likely used to replace the UU because of volume but I should be able to get this to run right. It spent a long time in use ultrasonic tank and has all the passages are cleared out which I think was a lot of it’s problem, plus it’s missing one idle channel hole washer which I can get from Cislak once I get my full list of parts I need together. The carburetor is in real good shape considering the pot-metal issues of that period and if I’m lucky enough to trip across the UUR at a reasonable price I might get it, but there again it might still have the same internal needs as a UU… fits Bugatti and Dusey, why couldn’t it have been Buick and Chevrolet?


    You are correct that the carb is often plugged in the internal passages and most people can’t get the plugs out to clean them. It is NOT easy to get them out. The UUR2 is much improved over the UU2. Interestingly there are FIVE diffrent UU2 bodies, and three diffrent UUR2 bodies, and they are not all interchangeable, but the “odd” ones are rather rare. Cleaning the unit and replacing worn shafts that leak air is 50 percent of thr battle. Getting correct internals is the other 50. John is a great resource and makes most every part you will need. Be sure to rebuild your fuel pump and clean the gas tank, or you will get to do the job over………..several times!


    Shafts have surprisingly little wear, and every plug came out after the second bath in the cleaner. Someone suggested that the ultrasonic vibrations would help loosen screws as it cleaned the passages, could not believe how easy it was to clean the front wheel bearings with it either. Definitely worth the investment.

    Tank was cleaned out and sealed by Milton Schilde and it’s running an electric pump with filter now as I don’t think the fuel pump has the correct arm for a Pierce – at least it doesn’t seem to be running on the cam like it should be and it doesn’t look like it was ever hooked up to a fuel line. The carburetor was also hooked up with rubber hoses which is a huge No-No right next to a manifold! Another thing to correct along this adventure.

    Took the valve covers off this morning and have been scraping oil turds out most of today. Funny thing that other than that usual crust of crud everywhere, the working parts look pretty good so far, but I haven’t written off a set of valves quite yet and rings are looking like a must with what I saw in the borescope. Might be a while before She is trustworthy, but I don’t have anything better to do with my time right now so back to scraping muck out…

    If you happen to have a picture of the correct fuel pump it would help me see if this is worth rebuilding or just blocking off.

    Thanks again



    Ed spelled my name wrong. You want to talk to Dave STEVENS about jetting. The “Dave Stephens” in the roster is a new member with an earlier car. I have a 1933 1247 and a 1936 1601. Both have been rejetted by John Cislak and the difference was quite noticeable. Richer is better.

    Rather than rebuild, ask John about rejetting and remember that his experience comes from a full time business, not just a hobbyist.

    Dave Stevens



    Sorry Dave……I’m a little out of it lately, too much work………..see you soon. Ed


    Mark, I’ve got a spreadsheet that lists applications for both UU2 and UUR-2 carbs with the various sizes required. I’ll email it to you.

    What year and model is your car?




    How about posting that on the Web site?



    A public thank you to Bill for the spreadsheet which was exactly what I needed! Everything but my main jets match up and I will be reaming those up to work.


    Since Ed mentioned my name, thought I’d make a comment. John Cislak rebuilt my carb (UUR-2) and mechanical fuel pump (sorry, I hate electric pumps) for my ’31 Model 43.

    The difference is incredible. Smoother starts and running, more power, better throttle response.

    My work must have been done before price increases, as it was very reasonable.


    Thank you David, the price I was quoted definitely scared me off. At some point I might have to get it done, but for now I am going through it myself. I pulled the fuel pump out and it is definitely not the right one for the car, that is something I might go looking for once I get through the engine and wiring but low on my current list. Still have not pulled the head off so a lot could change in the next couple weeks as the direction I will be going…

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